Bistable solenoid



Aug. 24, 1965 NQ R` KRAMER BISTABLE SOLENOID Filed Jan. ll, 1962 klo i m@ WM E m W m r f ww MW oC N 7.

UnitedStates Patent O i 3,2il2,8$6 BISTABLE SLENGIH) Nathan R. Kramer, Hartsdale, NY., assignerto Bulova Watch Company, Inc., New York, NX., a corporation of New York Filed Jan. 11, 1962, Ser. No. 165,690 8 Claims. (Cl. 317-171) This invention relates generally to electrically energized solenoids, and more particularly to a bistable solenoid whose armature can be actuated to either of two stable positions as a function of the polarity of an applied D.C. voltage.

With conventional D.C. energized solenoid structures,

the armature thereof will be driven from a static or deenergized position to an actuated position when voltage is applied. When the voltage is switched off, the armature will ordinarily be caused by a spring to return to its static position. In order therefore to hold the armature at a desired actuated position, it is necessary to maintain a constant energizing voltage or to provide me-chanical latching expedients, such as a detent or a toggle mechanism.

The primary object of the present invention is to provide a solenoid having an armature which can be actuated to either of two stable positions as a function of the applied D.C. power, the armature once driven remaining at the actuated position without requiring the continued application of power. Because of its bistable characteristics, the solenoid according to the invention will hereafter be referred to as a Binoid More specifically, it is an object of this invention to provide a Binoid having a polarized armature which is magnetically latched at its actuated position by reason of residual magnetism retained in its magnetic circuit. The Binoid is energized by a D.C. pulse and holds its actuated position after deenergization.

Another object of the invention is to afford a Binoid of the above-described type wherein the armature will return to its actuated position even if mechanically displaced from it, this memory characteristic remaining effective unless the armature is driven in the reverse direction to its second acuated position by a voltage pulse. In either of its two actuated positions, the Binoid exhibits a memory characteristic which can be erased only by reversal of the energizing voltage.

A significant feature of the invention resides in the fact that the Binoid has a higher operating force or torque and a greater effectivellength of travel or angle of travel as well as `flatter characteristic curves than standard solenoids of the equivalent size. The Binoid is highly efficient in operation and is adapted to perform operations of which conventional solenoids are incapable.

Briefly stated these objects are accomplished by a Binoid structure in which two stator coils are symmetrically arranged with respect to a polarized armature, each coil lying within a magnetic circuit having a pole piece adjacent a respective end of said armature. By energizing said -coils in magnetic opposition, the pole pieces of the two magnetic circuits assumea like polarization, hence one end of the polarized armature is repelled by reason of like polarizations whereas'the other end is attracted toward the pole of opposite polarization, producing a push-pull action to cause said armature to move in that direction.

Removal of the energizing voltage from the coils does not wipe out the polarization in the pole pieces of the respective magnetic circuits in that such polarization is maintained by the phenomenon of residual magnetism and the armature is held in its actuated position until 3,292,886 Patented Aug. 24, j 1965 ICC such time as a pulse is applied to the coils in the reverse direction. This pulse serves to erase the existing residual magnetism and to cause a reverse polarization in the pole pieces, which polarization is also maintained by residual magnetism after the power is cut off. Thus the Binoid is sta-ble at both actuated positions.

For a better understanding of the invention, as well as other objects and further features thereof, reference is made to the following detailed description to be read in conjunction with the accompanying drawing, wherein:

FIG. 1 is a longitudinal section taken through a Binoid in accordance with the invention;

FIG. 2 is an end view of the Binoid, and

FIG. 3 is the equivalent magnetic and electrical circuit.

Referring now to the drawings, and more particularly to FIGS. 1 and 2, the Binoid in accordance with the invention comprises a cylindrical casing 10, enclosed by end plates 11 and 12.V Symmetrically disposed within the casing are a pair of spaced annular stator coils 13 and 14, each coil lying adjacent an end plate.

Concentrically disposed within the casing is an arma-` ture assembly including a series of annular permanent magnets 15, 16 and 17 mounted on a shaft 18 which is reciprocally slidable within bushings 19 and 20, centrally inserted in the end plates. The portion 18a of the shaft on which the permanent magnets are supported is of reduced diameter relative to the end portion 18b slidable in bushing 19. The portion 18C passing through bushing 20 is further reduced in diameter, and received thereon in a sleeve 21 whose outer diameter corresponds to that of portion 181), the sleeve acting to clamp the magnets to the shaft.

The two coils are separated by an insulatingspacer 22 which occupies a central position in the casing, a metal ring 23 being interposed between coil 13 and the spacer and a metal ri-ng 24 being interposed between coil 14 and the spaces. The rings 23 and 24, the casing 10' and end plates 11 and 12 are all of magnetic material. The ring 23 and end plate 11 in combination with the related portion of casing 10 form a rst electro-magnetic circuit with respect to coil 13, the hub portion 11a of the end plate constituting a pole piece. Similarly, ring'24 and end plate 12 in combination with the related portion of casing 10 form a second electro-magnetic circuit with lrespect to coil 14, the hub portion 12a of the end plate constituting a pole piece.

While three magnets 15, 16 and 17 have been shown in stacked series position, their polarization being N-S, N-S and N-S respectively, an equivalent result may be obtained with a single elongated permanent magnet having Va north pole at one end adjacent pole pieceV 11a and a south pole adjacent pole piece 12a. The permanent magnets preferably are made of alloys such as Alnico, or such magnetic ceramic material as Ferroxcube.

The leads 13a and 14a for each of stator coils 13 and 14 are taken out through. suitable apertures in the casing, the coils being so wound and the leads being so connected that the coils are energized in magnetic opposition to create opposing fields. Consequently, as best seen schematically in FIG. 3, magnetic ux paths are created in the two magnetic circuits resulting in like polarization of the magnetic pole pieces 11a and 12a.

By way of example, we shall assume that when a posi- `tive pulse is applied at the input terminals to the coils, the pole piecesV are both polarized North, but when a negative `pulse is applied the polarization is South. In FIG. 3, the pole pieces are shown as both having an N polarization, whereas the left end of the polarized armature is N .and the right end is S. Thus the permanent magnet armature is magnetically repelled from one end where the polarizations are alike, land attracted at the ..9 other end where the polarizations are unlike, the armature being shifted toward the right by a push-pull action.

When the energizing voltage is cut off, the armature will still occupy its actuated position by reason of the phenomenon of residual magnetism which will maintain the pole pieces polarized, but with reduced magnetic strength. For a given voltage, the degree of residual magnetism will depend, as is well known, on the nature of materials used in the magnetic circuit and the number of ampere turns in the coils. It is possible therefore to design for a relatively low level or residual magnetism or a higher level.

For low levels of residual magnetism the armature will remain in the position assumed upon actuation with a holding force due primarily to the magnetic attraction between the permanent magnet and the oppositely polarized end plate. The greater the residual magnetism in this end plate, the more intense the attractive force.

if the armature is pushed to the opposite end of the stator where the polarities of the end plate and the permanent magnet are alike, it will encounter a repelling force. At low levels of residual magnetism, this repelling force will be less than the attractive force of the permanent magnet for the magnetic material of the end plate, and the armature will remain in the position to which it has been pushed.

However, increasing the residual magnetism augments the repelling force, with a net reduction in holding force. Hence by further increasing the level of residual magnetism, a point will be reached where the repelling force equals and then exceeds the force of attraction between the end of the permanent magnet armature and the like polarized end plate. If this force is also suflicient to overcome the friction at the bushings, the armature will return to the position to which it had originally been actuated, once the mechanical pushing pressure is released.

Thus the armature becomes stable in the electrically energized position, which position it remembers after the electrical energy is withdrawn such that it will return to this position even if mechanically moved away. In this manner the magnetic forces causing actuation of the armature also affords a memory as well as a magnetic latching action. v

In summary, the Binoid has two distinct characteristics, depending on the degree of residual magnetism developed after electrical energization.

(A) At high levels of residual magnetism exceeding the magnetic attraction between the polarized armature and the magnetic material of the end plate, the armature is magnetically latched and it is stable only in that position to which it has been electrically actuated, returning thereto if displaced from it mechanically.

(B) At low levels of residual magnetism wherein the residual magnetism is less than the magnetic attraction between the polarized armature and the magnetic material of the end plate, the armature will become magnetically latched in that position to which it has been actuated either electrically or mechanically.

The Binoid has a superior operating force or torque as compared to conventional solenoids of the same size, and it also has a greater length or angle of travel as well as a flatter characteristic curve. The reasons for these improved qualities are as follows: First, the repelling action between the permanent magnet armature and the electromagnetic stator at the start of the shaft stroke provides a strong initial force and push-pull action. Second, the permanent magnet armature yields a high attractive force at the end of the stroke due to the addition of a permanent magnet field to that of the electromagnet. Third, the movement of the shaft is not hampered by the actionV of a return spring, a reversal of motion being obtained by a positive electrical action requiring only a reversal in the polarity of the energizing voltage. Moreover, the field of the permanent magnet is reinforced` d at the end of each stroke due to its impact while in a strong sympathetic magnetic eld.

A similar Binoid action can be produced in a structure wherein the armature, while of magnetizable material, is not a permanent magnet, the armature being reciprocable within a single annular coil. Two fixed permanent magnets are positioned adjacent the opposite ends of the armature in axial alignment therewith, the pole pieces of these magnets being alike relative to the armature ends. When the coil is energized, the armature becomes polarized so that one end is attracted by one permanent magnet and is repelled by the other. Latching is effected by virtue of residual magnetism in the armature when the coil is deenergized, the action being similar to that disclosed in the previous embodiment.

While the Binoid has been disclosed as affording a linear reciprocating action, it will be appreciated that a rotary motion may also be obtained by the use of suitable linear to rotary devices of the type well known in the solenoid art, such as camming devices causing the shaft to rotate as it moves forwardly. It is therefore intended in the accompanying claims to cover all such modifications and changes as fall within the true spirit of the invention.

What is claimed is:

1. A bistable solenoid comprising a polarized armature magnetic means consisting of, first and second fixed electromagnets each having a coil and a pole piece adjacent one pole of said armature, said armature being axially reciproca'ble between said pole pieces, and means to energize said electromagnets simultaneously in opposition whereby said pole pieces have a like polarization and said armature is repelled by one and attracted by the other to provide a push-pull action, said pole pieces having sufficient residual magnetism such that upon de-energization said armature is maintained in its actuated position.

2. A solenoid, as set forth in claim 1, wherein said residual magnetism is at a level sufficiently high to produce a repelling force exceeding the attractive force between said polarized armature and the magnetic material of said pole piece.

3. A solenoid, `as set forth in claim 1, wherein said residua-l magnetism is at a low level producing a repelling yforce which is less than the attractive force between said polarized armature and the magnetic material of said pole piece.

4. A bistable solenoid comprising a cylindrical casing of Imagnetic material enclosed .by end @plates also of magnetic material and constituting pole pieces, a polarized armature disposed for axial reciprocation in said casing, a magnetic energizing means consisting of two fixed coils within said casing surrounding .said armature, one coil forming an electromagnet with one of said pole pieces, the other coil forming an electromagnet with the other pole piece, and means to energize said coils in opposition Iwhereby said pole pieces have a like polarizatlon.

5. A bistable solenoid comprising a cylindrical casing of magnetic material enclosed by end plates also of magnetic material and constituting pole pieces, a polarize/l armature disposed for axial reciprocation in said casing, a magnetic energizing means consisting of two fixed coils within said casing surrounding said armature, one coi-l forming an electromagnet with one of said pole pieces, the other coil forming an electromagnet with the other pole piece, and means to energize said coils in opposition whereby said pole pieces have a like polarization, said pole pieces being of a material possessing sufficient residual magnetism to act magnetically upon said armature when said coils are de-energized.

6. A bistable solenoid comprising a cylindrical casing of magnetic material enclosed by end plates also of such material, an armature assembly concentrically disposed Within said casing and constituted by a shaft; reciprocably slideable through said end plates and a cylindrical permanent magnet mounted on .said shaft, a magneti-c energizing means consisting of two fixed annular coils surrounding 4said permanent magnet Withinsaid casing and forming rst and second eleetromagnets with said pole pieces, and means to energize said coil-s in opposition whereby a like polarization is imparted to` said pole pieces.

`7. A bistable solenoid, as set forth in claim 6, further including `a magnetic ring adjacent each coil to form a magnetic circuit for lsaid coil which includes 'la pole piece 10 and `a por-tion of said casing.

v8. A .bistable solenoid as set forth in claim 6, wherein each of said pole pieces possess sufficient residual magnetism to produce a repelling force upon de-energization of the coil-s which exceeds the attractive force between the armature and the magnetic material of the pole piece.

References Cited by the Examiner UNITED STATES PATENTS '2,833,968 5/58 Karlsen 317-199 2,935,656 5/60 Baker 20G-87 3,126,501 3/64 Flora 317-1171 JOHN F. BURNS, Primary Examiner. 

1. A BISTABLE SOLENOID COMPRISING A POLARIZED ARMATURE MAGNETIC MEANS CONSISTING OF, FIRST AND SECOND FIXED ELECTROMAGNETS EACH HAVING A COIL AND A POLE PIECE ADJACENT ONE POLE OF SAID ARMATURE, SAID ARMATURE BEING AXIALLY RECIPROCABLE BETWEEN SAID POLE PIECES, AND MEANS TO ENERGIZE SAID ELECTROMAGNETS SIMULTANEOUSLY IN OPPOSITION WHEREBY SAID POLE PIECES HAVE A LIKE POLARIZATION AND SAID ARMATURE IS REPELLED BY ONE AND ATTRACTED BY THE OTHER TO PROVIDE A PUSH-PULL ACTION, SAID POLE PIECES HAVING SUFFICIENT RESIDUAL MAGNETISM SUCH THAT UPON DE-ENERGIZATION SAID ARMATURE IS MAINTAINED IN ITS ACTUATED POSITION. 